School buses are the primary mode of student transportation in North America. An estimated twenty-six million students in the United States alone are transported to school every school day via bus—over half the student population in the country. While school buses in countries outside of North America usually look like any other buses, North American school buses are distinctive for their yellow color.

It wasn’t always that way. The first school buses were horse-drawn carriages known as “school hacks” or “kid hacks.” They were being made by Wayne Works starting around 1886, though it’s possible they were around earlier. However, you probably wouldn’t see teams of school hacks in every American town; many children had to rely on walking (uphill both ways through the snow), farm wagons, or sledges to get to school.

In 1914, with the popularity of automobiles rising, Wayne Works moved on to automobile chassis, allowing eager students to get to school faster. With these “buses” students would sit on the perimeter of the bus facing inward rather than toward the front as they do today. Afterwards, the Blue Bird Company began constructing a design for a bus that more closely resembles the buses that we know today, though they still had a long way to go.

In the 1930s, school buses underwent a series of standardisations. Before this time, school buses were mostly vehicles that had been repurposed as a mode of transportation for a number of students to and from school. A “California top” design—the rounded roof of the bus—patented by Gillig Bros was widely used, but parents were still worried about school bus safety and there was interest in standardizing the way that children got to and from school.

In 1939, Dr. Frank Cyr rose to the occasion and organized a conference at the University of Manhattan in order to develop school bus standards. Prior to this, he had travelled the country observing the various types of school buses in use and safety precautions that they used, if any. The conference was funded by a $5000 grant (about $81,571 today) from the Rockefeller Foundation and attracted transportation officials from all 48 states in the Union at the time.

The result of the conference was 44 national standards for school buses being developed. One of these standards was school buses should be “national school bus glossy yellow”. Initially called “national school bus chrome,” the color was chosen because of its attention-grabbing qualities. It gets noticed faster than any other color. For instance, in one’s peripheral vision, studies have shown that humans notice the color yellow 1.24 times faster than another eye-catching color, red. Yellow is also particularly visible in the early morning and evening light, when school buses usually operate. The hope was that people would see the color of the bus quickly and know to slow down and be mindful of the children on board.

Thirty-five states within the U.S. switched to painting their buses this color soon after the conference, as did certain regions of Canada. But it wasn’t until 1974 that all school buses in the United States were painted this color.

While the standards are tweaked from time to time, the color of the buses isn’t likely to be one of those standards changed any time soon according to Bob Riley, the executive director of the National Association of State Directors of Pupil Transportation Services (that’s quite a mouthful, Bob):

You can’t buy a bus that doesn’t meet that [color] formula… If they had to do it today, who knows if it would be the same, because now they have brighter, more noticeable things. Think of the vests highway workers wear. Obviously, they’re even more noticeable than national school bus chrome yellow. But the rationale for maintaining that color is its universal acceptance. We’ve all been born and raised knowing what that is.

With all this talk about safety on school buses, you might be wondering why there aren’t seat belts on most of them. (School buses weighing under 10,000 pounds are required to have them, but they are the only ones, aside from the fact that the driver’s seat always has a seatbelt.) In a nutshell, cost and the fact that school buses are already pretty amazingly safe. For starters, the closely spaced seats (the bane of the knees of tall students) are also shock-absorbent and able to protect children effectively enough according to studies by the National Transportation Safety Board and National Academy of Sciences. The seat design and spacing more or less functions as a “protective envelope.”

School buses are also some of the larger vehicles on the road and they aren’t typically driven very fast, further helping make them safe without seatbelts. How safe? Only about 11 students die per year in school bus crashes. Mile for mile, this is about 1/7th the average rate of deaths in all other automobile accidents.

Of course, the seats won’t do much if the bus tips over on its side. But it would cost an estimated $800 million to outfit every school bus in the U.S. with seatbelts. If this were the only factor, it still might get pushed through, as “think of the children” is every politician’s favorite phrase for getting expensive things done, whether the thing proposed is a good idea or not. In this case, they could even make it much less expensive up front by simply requiring that all new school buses have seat belts, then over the decades the seat belt-less buses would be naturally phased out. The new buses would cost a titch more due to adding seat belts, but much less than modifying existing buses and this would also spread the cost out over years.

The crux is that it isn’t clear at all whether all this effort would accomplish anything. There is some evidence that, for various reasons, the actual number of injuries might actually increase if school buses had seatbelts. From a practical standpoint, there is also the difficulty of a bus driver making sure all the kids are wearing their belts. With this issue, the uncertainty that it would even make kids safer, and the cost, getting seatbelts in school buses isn’t exactly top priority for the organizations involved.

One of the founders of UPS originally wanted the trucks to be yellow, instead of brown. He was eventually convinced to make them brown by Charlie Soderstrom. Soderstrom pointed out that yellow trucks would be impossible to keep clean. Railroad cars are often brown for this same reason.

“School bus yellow” is actually used in Europe for many mail and other services (some of which used the color long before it was associated with school buses in the US). Sweden used it for their postal service between 1923 and 1991, and it was also a popular color choice for post services in Germany and Switzerland. It’s used in Hungary on some buses and coaches. As for other school buses, a few school districts in the UK have adapted the color for their own buses.

School Bus Yellow is recorded as Federal Standard No. 595a, Color 13432 with both the National Highway Traffic Safety Administration and the National Institute of Standards and Technology.